Overlapping fiber gratings
AssigneeIntuitive Surgical Operations, Inc.
InventorsMark E. Froggatt, Brooks Childers
Life of this patent
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Abstract
Described are optical fibers, e.g., for use in stress-sensing or shape-sensing applications, that use overlapping grating configurations with chirped gratings to facilitate strain delay registration. In accordance with various embodiments, a fiber core may, for instance, have two overlapping sets of chirped gratings that differ in the direction of the chirp between the first and second sets, or a set of chirped gratings overlapping with a single-frequency grating. Also described are strain sensing systems and associated computational methods employing optical fibers with overlapping gratings.
Claims20
A strain measurement system comprising:
- an optical fiber comprising a fiber core including overlapping first and second sets of gratings, the first and second overlapping sets of gratings having chirp rates that differ in direction or in magnitude or in both direction and magnitude;
- interrogation means for coupling light into the fiber core and measuring a time-domain reflection signal resulting from reflections of the light off the overlapping first and second sets of gratings;
- and
- computational processing means comprising:
- conversion means for converting the measured time-domain reflection signal into a plurality of measurement reflection spectra associated with different time delays;
- mapping means for mapping each measurement reflection spectrum of the plurality of measurement reflection spectra to a reference reflection spectrum of a plurality of reference reflection spectra and to an associated frequency shift between the measurement reflection spectrum and the reference reflection spectrum, whereby the associated frequency shift is associated with a unique location corresponding to the reference reflection spectrum;
- and
- strain determination means for determining, based on the associated frequency shifts, strain in the fiber core along the optical fiber.
A strain measurement system comprising:
- an optical fiber comprising a fiber core having overlapping first and second sets of gratings, wherein the first set of gratings comprises one or more chirped gratings extending over a section of the fiber, and wherein the second set of gratings comprises one or more gratings extending over the section of the fiber, the one or more gratings of the second set of gratings not being chirped like the one or more chirped gratings of the first set of gratings;
- interrogation means for coupling light into the fiber core and measuring reflection signals resulting from combined reflections of the light off the first and second sets of gratings;
- and
- computational processing means comprising:
- conversion means for converting the measured reflection signals to time-delay-dependent reflection spectra,
- correlation means for correlating the time-delay-dependent reflection spectra with time-delay-dependent reference reflection spectra to determine correlation maxima across time delay and frequency, each correlation maximum corresponding to a pair of a first spectrum of the time-delay-dependent reflection spectra and a second spectrum of the time-delay-dependent reference reflection spectra, and to a frequency shift between the first spectrum and the second spectrum of the pair, and,
- strain determination means for computing, for each correlation maximum of the correlation maxima, a strain at a position along the fiber associated with the second spectrum corresponding to the correlation maximum from an associated frequency shift.
An optical fiber sensor comprising:
- a fiber core comprising:
- a first set of gratings, the first set of gratings being chirped, and
- a second set of gratings overlapping with the first set of gratings in at least a first section of the fiber core, wherein the first and second sets of gratings differ in at least one characteristic selected from the group consisting of:
- being chirped or not chirped, chirp direction, and magnitude.
Dependencies are inferred from the claim text.